Insert new excel sheets in a file - Issue with ranges - Need a CLEVER process!

Hello!
So, this is my situation - I have developed an excel tool, which makes a lot of useful calculations for me. The calculations come from 10 other sheets, which are in the same file.
So, in general, I have an excel file with about 20 sheets - 10 make the calculations and 10 serve as input data.

My issue is, that every month I get new input data (10 sheets) and I need a way to integrate them to the tool and to make it work.

What I do now:
1. I take every sheet of the 10 sheets for "input data" and I rename it manually, putting "old_" in front.
2. Excel automatically changes the formulas in a way to reference this "old_" name. (This is actually my problem!)
3. I insert the 10 sheets with the new data.
4. I press about 10 times "Replace" and I replace the formulas with "old_" to the new sheet.
5. It takes me a lot of time... And I do not like it

Any ideas for process improvement? I understand also macros, so you can give an idea there. I can write a macro, which does exactly the same process for me, (the work is actually 80% macro recorder and 5% deleting useless code actually ) but there should be a more clever way in Excel to do it... Really, something like turning off automatical references or something...

Any ideas are welcomed!

Thank you!

Change your formulas to:

Formula:

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This will then preserve the original sheet names in the formula.

Thank you, OllyXLS!
That is a good option, indeed!
Any other options would be appreciated.
Btw, any idea why I get the mistake #REF!, when I use the INDIRECT formula?

edit: I think it is because of the QUOTES missing

If you're getting a #REF! error:

Make sure your formula is enclosed by quotation marks. e.g.

Formula:

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Make sure your sheet and cell references are valid.

Thanks once again, it works now.

Anyway, other options would be appreciated... Anything to make it even faster ....
(Although I have written a macro to put every formula to =INDIRECT("") automatically... and I really do not know what can be faster )
Anyhow ... ?